Purpose: This study was to estimate the effectiveness of an intervention program using the trans-theoretical model on the stages of change, the process of change, decisional balance, self-efficacy, the levels of medication adherence, and blood pressure difference. Methods: A similar experiment was conducted using a nonequivalent control group pre- and post-test design. The study subjects were 108 hypertensive patients. The program was administered to the experimental group while educational materials were given to the control group. Descriptive analysis, 2-test, t-test, and repeated measures ANOVA were used with SPSS 17.0 to analyze collected data. Results: After treatment with this program, the experimental group showed stage of change ($x^2=52.917$, p<.001), cognitive (F=13,528, p<.001), behavioral process of change (F=10.808, p<.001), benefits (F=5.569, p=.012), loss of medication adherence (F=15.661, p<.001), self-efficacy (F=5.407, p=.011), levels of medication adherence (F=51.442, p<.001). Conclusion: There was a significant improvement in the experimental group who participated in the TTM medication adherence intervention program. Given that this intervention program motivated and stimulated hypertensive patients to adhere to the prescribed medications, the TTM medication adherence intervention program is expected to be an effective and practical intervention method for health improvement.